[R] [External] Building promise evaluations

[iuke-tier@ey m@iii@g oii uiow@@edu]

Promises are an internal implementation detail that could change or
even disappear at any time. They should not be directly visible at the
R or package C level, the fact that they currently might be in some
case notwithstanding. delayedAssign is the only tool you can use for
programmatically creating delayed bindings in an environment (which
happen to currently be implemented via promises, but that could
change). Deferred evaluations should only exist in environments, not
anywhere else. So you should arrange what your are trying to do to
create a deferred binding in an environment in which you evaluate your
call.

Best,

luke

On Thu, 12 May 2022, Andrew Simmons wrote:

> Hello,
>
>
> I was hoping to build some promise evaluations and put them into a
> call to be evaluated, but it doesn't seem as though there's an easy
> way to build the promises. I can see from the r-source repository that
> the C function mkPROMISE defined in Defn.h is what I need, but that
> file doesn't seem to be included when downloaded (R.home("include")
> does not contain this file).
>
> I'm not particular about whether this has to be done at the R level or
> at the C level, any solution is good to me.
>
> Just in case anyone is wondering "why don't you just evaluate the call
> in the same environment as you would assign to the promises?", I want
> to evaluate the function and the first argument in my own environment,
> and the rest of the arguments in an environment of the user's
> choosing, and I can't do that without promises. Another question "why
> don't you use the argument ... in your function to pass arguments
> which will be evaluated in the user's environment?", I can't do that
> either. The user's arguments are provided as a string from which the R
> code is extracted, parsed, and then I can make use of them. Any help
> is greatly appreciated!
>
>
> Regards,
>    Andrew Simmons
>
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-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu